[llvm-dev] Semantics of LLVM IR intermediate variables
James Clarke via llvm-dev
llvm-dev at lists.llvm.org
Fri Oct 25 16:17:02 PDT 2019
On Fri, Oct 25, 2019 at 08:23:25AM +0000, Mehdi AMINI via llvm-dev at lists.llvm.org wrote:
> On Fri, Oct 25, 2019 at 12:57 AM Jason Thomas via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> > Hi all,
> > This question may sound stupid, but every time I look at the IR, I take
> > some time to convince myself the following:
> > The following C source code:
> > 1 int x ;
> > 2 int * p ;
> > 3 p = & x ;
> > when compiled to LLVM IR using clang generates the following instructions:
> > 1 % x = alloca i32 , align 4
> > 2 % p = alloca i32 * , align 8
> > 3 store i32 * %x , i32 ** %p , align 8
> > All the local variables in the C source code, i.e. 'x' and 'p' are
> > pointers now, in fact they are pointers with one level deeper nesting
> > level. What I mean is, 'x' is an 'int' in the C source, but '%x' is 'i32*'.
> > 'p' is 'int*' in the C source, but '%p' is 'i32**'. Doesn't it make the IR
> > naming convention a misnoer compared to their C counterpart? Shouldn't
> > '%x.addr' or '%p.addr' a better naming convention? Is there anything that I
> > am missing?
> You're right that the name isn't the most accurate from a clang point of
> view, redirecting to cfe-dev@ if anyone has an opinion from the clang side.
This is, however, consistent with global variables, where @foo is &foo
in the C source, which also matches what the linker's view is (where the
value of a symbol is its address).
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